Magnetic recording media widely used generally contain a thermoplastic resin such as a vinyl chloridevinyl acetate resin, a vinyl chloride-vinylidene chloride resin, a cellulose resin, an acetal resin, a urethane resin or an acrylonitrile butadiene resin, alone or in combination, as a binder. However, such magnetic recording media or magnetic tapes suffer inferior wear resistance of the magnetic layer and stains in the tape path.
It is known that a thermosetting resin such as a melamine resin or a urea resin can be used as a binder and that a binder which is cross-linked by a chemical reaction such as an isocyanate compound or an epoxy compound can be added to the above described thermoplastic resin. However, the use of the cross-linkable binder is accompanied with such defects that (1) a resin solution having dispersed therein magnetic particles has poor storage stability, that is, the pot life is short, the physical properties of the magnetic coating composition are not homogeneous and the magnetic tape does not have a homogeneous quality, and that (2) after the magnetic coating composition is coated and dried, heat treatment for hardening the coated layer is necessary. That is, a long period of time for manufacturing the product is necessary.
U.S. Pat. Nos. 3,871,908 and 4,443,490, Japanese Patent Publication (examined) No. 12423/1972, Japanese Patent Publication (unexamined) Nos. 15104/1972 and 77433/1975 disclose methods for preparing a magnetic recording medium by irradiating electron beams on the coating composition comprising an oligomer or a monomer of arcylic ester as a binder for hardening after drying in order to remove the above-described disadvantages. However, a magnetic recording medium having excellent electromagnetic properties and running durability cannot be obtained by the above-described method.
Recently, it has been required that the support of magnetic tapes be as thin as possible in order to allow recording for a long time, and the mechanical properties of the magnetic layer are rquired to be improved. For example, magnetic tapes are required to be used under severe conditions as video cassette recorders become multifunctional. However, heretofore, satisfactory physical properties meeting the above-described requirements have not been provided with a magnetic layer.